The present invention relates to an apparatus for recognizing electronic components and more particularly to an apparatus for photographing and recognizing an electronic component by back lighting or front lighting without changing the vacuum nozzle according to the kind of component.
In Japanese Patent Publication No. Hei 8-24234 (U.S. Pat. No. 5,131,139), a component mounting machine is described which has a nozzle with a larger outer size than that of a component absorbed to the nozzle. A tapered surface is formed on the lower portion of the nozzle as a light diffusing surface and the size of the lower end of the nozzle is smaller than that of the component. A light source is placed under the nozzle which radiates light upwardly towards a diffuser means disposed above the nozzle. The light is then diffused downward to a tapered surface on the nozzle, which becomes bright. The absorbed component is clearly observed as a black silhouette inside the bright tapered surface by a camera disposed below the moving path of the nozzle.
The Japanese Utility Model Registration No. 2520596 (Laid-Open Publication No. Hei 4-631771) describes a vacuum nozzle which has a tapered, mirror-finished surface. The reflected light from the absorbed component is observed by a camera disposed opposite to the component. This arrangement prevents the reflected light from the tapered surface from being observed by the camera as incident light.
Japanese Patent Publication No. Hei 4-46000 describes an apparatus for detecting the position of a component which includes two light sources. One is placed above the absorbed component and the other is placed below the absorbed component. The light from the upper light source is radiated at the component through a diffusion plate and the component is photographed by a camera disposed under the component (which arrangement is called "back lighting"). The light from the lower light source is radiated at the component through another diffusion plate with an aperture therein. The reflected light from the component is then photographed through the aperture by the camera (which arrangement is called "front lighting").
Several problems arise, however, in using the structure described in U.S. Pat. No. 5,131,139. Many types of components are used in a component mounting machine, such as rectangular chips, SOP (Small Outline Package), QFP (Quad Flat Package), MELF (Metal Electrode Face), PLCC (Plastic Leaded Chip Carrier), SOJ (Small Outline J-leaded package), BGA (Ball Grid Array package), etc. Among these components, such components as rectangular chips, SOP, QFP, MELF, etc. can be recognized precisely, but PLCC, SOJ, BGA, etc., which have their leads on the back side of the components, are difficult to recognize accurately since only back lighting is usable with this structure. Therefore, other means of capturing the reflected image of these components, (front lighting, for example) is required in order to capture the image precisely. Another disadvantage of this structure is that the light source disposed below the component is mounted in a ring arrangement, which needs a wider area. Furthermore, in order to confine the light source to a small area by using a smaller diameter ring light with narrow directivity, additional elements like lenses would be needed, which leads to a high cost for the apparatus.
With the structure described in Japanese Utility Model Registration No. 2520596, components such as rectangular chips, SOP, QFP, etc. can be recognized but with less accuracy than by recognizing them by the aforementioned back lighting arrangement. PLCC, SOJ, BGA, etc. components are possible to recognize, but cylindrical components like MELF are difficult to recognize with high accuracy because only front lighting can be used. Moreover, a diffusion plate must be placed over the nozzle so that only the reflected light from the component is incident on the camera, eliminating other reflected light, or the area of the mirrored tapered surface of the nozzle must be wider than that of the recognizing means, which leads to a higher cost apparatus.
In both of the aforementioned structures, the size of the lower end of the nozzle must be smaller than that of the component. Therefore, the mechanical strength of the nozzle is weakened when a tiny size component is to be absorbed.
Still further problems arise when the structure described in the Japanese Patent Publication No. Hei 4-46000 is adopted, although this structure has both back lighting means and front lighting means. Both of the light sources have to be diffused by diffusion plates when lighting the absorbed component. While there is enough space under the nozzle, it is difficult to find enough space to mount the light source and the diffusion plate above the nozzle, and so this structure requires a complicated arrangement.
It is therefore an object of the present invention to provide an apparatus for recognizing precisely the component absorbed by the vacuum nozzle by using back lighting or front lighting without additional diffusion plates.
In order to solve the problems mentioned above, the present invention employs an apparatus for photographing and recognizing an absorbed component comprising a vacuum nozzle which includes a main body portion having a larger outer size than that of the absorbed component and a tapered surface formed at the lower portion of the nozzle as a light diffusing surface, a first light source and a second light source for lighting the absorbed component. The tapered surface is formed in such a manner that the absorbed component is lighted by back lighting from the first light source reflected off the tapered surface or is lighted by front lighting from the second light source, according to the type of the component.
With the arrangement described above, the direction of the diffused light on the tapered surface is changed according to the selection of one of the two light sources, since the tapered surface is formed at a predetermined angle with the nozzle axis. Thus, precise recognition can be attained by employing back lighting or front lighting of the component as appropriate.
This tapered surface can be made by sandblasting after machining (for example, by lathing) in order to get the desired reflecting/diffusing characteristics.
When recognizing the absorbed component, only the image taken adjacent to the detected contour of the tapered surface, which includes the image of the absorbed component, is processed. Therefore, image processing time and the area of the tapered surface can be reduced.
If the suction surface at the lower end of the nozzle is made of light absorbing material (deluster coated material or ceramic), the size of the suction surface can be larger than that of the absorbed component. Therefore, the mechanical strength of the nozzle can be increased in case a tiny size component is to be absorbed.
In still another embodiment, a plurality of light sources for back lighting are mounted on four walls separated by different sized spaces from each other. The light sources surround the vacuum nozzle for lighting the tapered surface with even brightness. This arrangement lights the absorbed component evenly by back lighting reflected off the tapered surface. This method can improve the accuracy of recognizing the component.
The first light sources for back lighting as described above are disposed at multiple heights in the direction of the up/down movement of the vacuum nozzle. Predetermined light sources facing the tapered surface are selectively turned on according to the up/down movement of the vacuum nozzle in response to the thickness of the absorbed component. This means of back lighting can avoid excessive light intensity on unnecessary portions of the tapered surface 5, prevent bad effects in recognition of the component, and results in a reduction of power consumption.